1. Field of the Invention
The present invention relates to a structure of a vehicular active antenna system and a satellite tracking method with the system, and more particularly, to a structure of a vehicular active antenna system and a satellite tracking method with the system having a satellite tracking function in order to receive signals for a satellite broadcasting or a satellite communication in a vehicles.
2. Discussion of the Related Art
In the prior art, in order to receive signals for satellite broadcasting and satellite communication in a vehicle, an antenna system having a fixed azimuth angle is used and the antenna system is controlled two-dimensionally and mechanically. However, in this case control of tracking speed and posture is complicated. On the contrary, in the present invention a phased array antenna system is used and the phases of unit antenna elements are controlled two-dimensionally.
FIG. 2 shows a structure of a phased array antenna according to a prior art.
Each of n unit antenna elements 21, 21-1, . . . , 21-n has an initial steering phase value, and a satellite signal receiver 22 determines magnitudes of received satellite signals and then transfers a received signal intensity information 23 to a satellite tracking processor 26. The information is provided to a tracking calculation processing program block 27 which performs satellite tracking, control selection, power control and power blocking control. The tracking calculation processing program block 27 discriminates the state and calculates accurate satellite steerings, and then transfers a beam steering control signal 28 to the unit antenna elements in order that the phases of the unit antenna elements are delayed such that the antenna elements are oriented toward a desired satellite steering. In this case, in order to determine a satellite tracking steering and a tracking velocity, a rotation angular rate information of a mobile from an angular rate sensor 24 are also processed and determined concurrently.
FIG. 3 shows a functional view for illustrating a method for forming a single beam in a conventional phased array antenna, and particularly, a method for forming a single beam of an antenna oriented at a desired antenna steering angle .theta..degree. at which a reception satellite signal 31 is incident.
If phase delay values are provided to each of unit phase shifters B1 to Bn using beam steering control signals 28 (see from FIG. 2), each of unit antenna elements A1 to An is delayed by phase differences .DELTA..PHI. among them in order that received satellite signals reach an equal phase simultaneously. In this case, the delay values relates to a distance difference d 32 between the antenna elements. The satellite signals reach the unit antennas to which the equal phase of signals are received and are coupled in a signal power combiner 33, becoming final antenna received satellite broadcasting signals 34 before reaching a receiver.
FIG. 4 shows a graph for illustrating a satellite tracking method in a prior phased array antenna, and particularly, a tracking method by which a satellite tracking processor (see 26 in FIG. 2) is used for satellite tracking. The antenna has a characteristic curve of magnitudes of antenna received satellite broadcasting signals according to the beam steering angles .theta. and .PHI. at a mobile position, and since the curve has a maximum value M, the satellite tracking processor (see 26 in FIG. 2) is programmed to detect magnitudes of the received satellite broadcasting signals (34 in FIG. 3) and always to trace the maximum value.
In such a phased array antenna, the number of phase-controlled elements are too many, and thus the control is complicated and the manufacturing cost becomes high. In addition, since either a mono-pulse satellite tracking mode or a step-tracking mode is applied to the satellite tracking, accuracy of the satellite tracking becomes low and loss of the tracking signal becomes high. Also, since a method for sensing a rotating velocity together with a steering using received signals and then calculating a relative steering is used for sensing the movement of the antennas, there are problems that when a vehicle with a mobile terminal passes through an area blocking the satellite signals for a long time, accuracy is lowered after recovering the satellite tracking and it needs a long time for passing through the blocking area.